The present invention relates to a combustion-type power tool, and more particularly, to such a power tool enhancing combustion efficiency.
In a conventional combustion-type driving tool such as a nail gun, a gaseous fuel injected into a combustion chamber is ignited, and the combusted fuel is agitated by an axial fan disposed in a combustion chamber to promote combustion, so that gas expansion in the combustion chamber causes a linear momentum of a piston. By the movement of the piston, a nail is driven into a workpiece. Such conventional tool is disclosed in U.S. Pat. Nos. 4,483,280 and 5,197,646.
In the above-described conventional combustion type power tool, combustion speed is increased through the agitation by the fan. Here, turbulence can be improved and accordingly combustion speed is increased by the employment of the fan in comparison with a case where no fan is provided. However, the conventional fan has a configuration to generate a smooth flow. As a result, sufficient combustion speed has not been attained, and insufficient driving energy results.
During rotation of the axial fan, the most turbulent area of the combustion gas is located at a leading edge side of each fan blade in a rotating direction of the fan. However, in the conventional combustion type power tool, a distance between neighboring leading edges of the neighboring fan blades is too large due to the shortage of the number of fan blades. Consequently, relatively long time period is required for the ignited flame having been reached one leading edge side of the fan blade to reach the next leading edge side of the next fan blade even as a result of immediate start of combustion and expansion. Thus, combustion speed through an entire space of the combustion chamber may be lowered, to render the driving energy insufficient.